Mems proof mass with split z-axis portions

ABSTRACT

This document discusses among other things apparatus and methods for a proof mass including split z-axis portions. An example proof mass can include a center portion configured to anchor the proof-mass to an adjacent layer, a first z-axis portion configure to rotate about a first axis using a first hinge, the first axis parallel to an x-y plane orthogonal to a z-axis, a second z-axis portion configure to rotate about a second axis using a second hinge, the second axis parallel to the x-y plane, wherein the first z-axis portion is configured to rotate independent of the second z-axis portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/363,537, filed on Feb. 1, 2012, which is incorporated by referenceherein in its entirety.

This application is related to Acar, International Application No.PCT/US2011/052065, entitled “MICROMACHINED MONOLITHIC 3-AXIS GYROSCOPEWITH SINGLE DRIVE,” filed on Sep. 18, 2011, which claims the benefit ofpriority to Acar, U.S. Provisional Patent Application Ser. No.61/384,245, entitled “MICROMACHINED MONOLITHIC 3-AXIS GYROSCOPE WITHSINGLE DRIVE,” filed on Sep. 18, 2010, and to Acar, InternationalApplication No. PCT/US2011/052064, entitled “MICROMACHINED 3-AXISACCELEROMETER WITH A SINGLE PROOF-MASS,” filed on Sep. 18, 2011, whichclaims the benefit of priority of Acar, U.S. Provisional PatentApplication Ser. No. 61/384,246, entitled “MICROMACHINED 3-AXISACCELEROMETER WITH A SINGLE PROOF-MASS,” filed on Sep. 18, 2010, each ofwhich is hereby incorporated by reference herein in its entirety.

BACKGROUND

Several single-axis or multi-axis micromachined accelerometer structureshave been integrated into a system to form various sensors. As the sizeof such sensors becomes smaller and the desired sensitivity more robust,small scale stresses on certain components of the accelerometer candetract from the accuracy of the sensors.

Overview

This document discusses, among other things, apparatus and methods for aproof mass including split z-axis portions. An example proof mass caninclude a center portion configured to anchor the proof-mass to anadjacent layer, a first z-axis portion configure to rotate about a firstaxis using a first hinge, the first axis parallel to an x-y planeorthogonal to a z-axis, a second z-axis portion configure to rotateabout a second axis using a second hinge, the second axis parallel tothe x-y plane, wherein the first z-axis portion is configured to rotateindependent of the second z-axis portion.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIGS. 1A, 2A and 3A illustrate generally example proof masses with splitz-axis portions.

FIGS. 1B, 2B, and 3B illustrate generally perspective views of proofmasses with split z-axis portions.

FIG. 4 illustrates generally an example gyroscope and accelerometersensor including an accelerometer proof mass with split z-axis portions.

FIG. 5 illustrates generally a schematic cross sectional view of anexample 3-degrees-of-freedom (3-DOF) inertial measurement unit (IMU)including an example proof mass with split z-axis portions.

DETAILED DESCRIPTION

FIG. 1A illustrates generally an example of a proof mass 100 thatincludes a split z-axis portion. In certain examples, the proof mass 100can be used in a sensor for detecting acceleration. In certain examples,the proof mass 100 can be micromachined from a device layer material.For reference herein, the major surfaces of the proof mass lie in an x-yplane and a z-axis direction can be orthogonal to each x-y plane. Incertain examples, a sensor can include a chip scale package wherein theproof mass 100 can be positioned between a via layer and a cap layer. Incertain examples, the device layer can be positioned within a vacuumcavity between the cap layer and the via layer. The cavity canaccommodate out-of-plane movement of portions of the proof mass 100. Incertain examples, the proof mass 100 can include a central portion 101and first and second z-axis portions 102, 103. In some examples, thecentral portion 101 can include an anchor region 104. The anchor region104 can be used to anchor the proof mass 100 to an adjacent layer of thesensor, such as the via layer, in certain examples. In an example, amoment arm 105 of the first z-axis portion 102 can be coupled to thecentral portion 101 by a first hinge 106. The first hinge 106 can allowthe moment arm 105 of the first z-axis portion 102 to rotate about anx-axis. In an example, a moment arm 107 of the second z-axis portion 103can be coupled to the central portion 101 by a second hinge 108. Thesecond hinge 108 can allow the moment arm 107 of the second z-axisportion 103 to rotate about an x-axis. Acceleration of the proof mass100 along the z-axis can cause one or both of the z-axis proof massportions 102, 103 to rotate about a central axis of the hinge 106, 108coupling each z-axis portion 102, 103 to the central portion 101 of theproof mass 100. In certain examples, acceleration of the proof mass 100along the z-axis can cause the first z-axis portion 102 to rotate in afirst direction and the second z-axis portion 103 to rotate in a seconddirection. In an example, an end of the first z-axis portion 102 canrotate away from an adjacent end of the second z-axis portion 103 for agiven acceleration along the z-axis.

In certain examples the proof mass 100 can be used to detectacceleration along multiple axes. In some examples, the proof mass caninclude electrodes to detect acceleration along the x and y axes. Theexample illustrated in FIG. 1A includes x-axis flexure bearings 109 thatcan respond to acceleration along an x direction, and y-axis flexurebearings 110 that can respond to acceleration along a y direction.Electrodes to detect the deformation of the x and y flexure bearings arenot shown in FIG. 1A.

FIG. 1B illustrates a generally a perspective view of an example proofmass 100 including a split z-axis portion. The proof mass 100 includes acentral portion 101, a first z-axis portion 102, a first hinge 106, asecond z-axis portion 103, and a second hinge 108. The first hinge 106can couple the moment arm 105 of the first z-axis portion to the centralportion 101. The second hinge 103 can couple the moment arm 107 of thesecond z-axis portion 103 to the central portion 101. In the illustratedexample, the second hinge 108 is located at an opposite corner of thecentral portion 101 from the first hinge 106. In certain examples, thehinges 106, 108 are asymmetrically coupled to their respective z-axisportion moment arm 105, 107 to allow adjacent ends of the z-axisportions 102, 103 to move in opposite, out-of-plane directions for agiven acceleration along the z-axis. In certain examples, each z-axisportion 102, 103 includes a first electrode end (Z+) coupled to a secondelectrode end (Z−) by the moment arm 105, 107. In certain examples, anelectrode can be formed at each electrode end. In some examples, aportion of an electrode can be formed on a major surface of each z-axisportion of the proof mass 100 at each electrode end. In some examples, asecond portion of each electrode can be formed on the via layer neareach electrode end of each z-axis portion 102, 103. Each z-axis portion102, 103 can be associated with a pair of electrodes. In certainexamples, the pairs of electrodes can be complementary. Complementaryelectrodes can assist in eliminating residual effects of proof massstress that can be present during operation of the sensor, that can bepresent due to manufacturing variations of the proof mass, or that canbe present due to assembly operations of the sensor. In certainexamples, the complementary pairs of electrodes, located near theextents of the proof mass, can allow efficient cancellation of packagingand temperature effects that can cause asymmetric deformations on theopposite sides of the proof-mass. Packaging and temperature stressesthat can cause different deformations on each side of the mass, can alsocause asymmetric capacitance changes on each side of the proof mass.These capacitance changes can cause a net bias that the complimentaryz-axis electrodes can efficiently cancel.

FIG. 2A illustrates generally an example proof mass 200 including splitz-axis portions 202, 203, a central portion 201 and hinges 206, 216,208, 218 for coupling the split z-axis portions 202, 203 to the centralportion 201. In certain examples, the proof mass 200 can be anchored toan adjacent sensor layer via an anchor region 204 of the central portion201 of the proof mass 200. In certain examples, the proof mass 200 canbe used to measure acceleration along a z-axis using out-of-planemovement of the split z-axis portions 202, 203 of the proof mass 200. Insome examples, the proof mass 200 can be used to detect accelerationalong multiple axes. In some examples, the proof mass 200 can includeportions of electrodes 211, 212 to detect acceleration along the x and yaxes. The example proof mass of FIG. 2A includes x-axis flexure bearings209 that can respond to acceleration along an x direction, and y-axisflexure bearings 210 that can respond to acceleration along a ydirection. Electrodes to detect the deformation of the x and y flexurebearings 209, 210 can be formed, in part, using the proof mass 200, andstator structures 213, 214 anchored to an adjacent layer of anacceleration sensor. In certain examples, the split z-axis portions 203,203 of the proof mass 200 can include a first z-axis portion 202 and asecond z-axis portion 203. The first z-axis portion 202 can be coupledto the central portion 201 using a first hinge 206 and a second hinge216. The second z-axis portion 203 can be coupled to the central portion201 of the proof mass 200 using a third hinge 208 and a fourth hinge218. In certain examples, the use of two hinges 206 and 216, 208 and 218to couple one of the z-axis portions 202, 203 to the central portion 201can make the z-axis portion more resistant to wobble or movements in thex or y directions. Movement of the split z-axis portions 202, 203 in thex or y directions can cause misalignment of the z-axis electrodes and,in turn, can lead to less accurate z-axis acceleration measurement.

In certain examples, the each pair of hinges 206 and 216, 208 and 218can asymmetrically couple their respective z-axis portion 202, 203 tothe central portion 201 to allow adjacent ends of the z-axis portions tomove in opposite, out-of-plane directions for a given acceleration alongthe z-axis. In certain examples, each z-axis portion includes a firstelectrode end (Z+) and a second electrode end (Z−). In certain examples,an electrode can be formed at each electrode end. In some examples, aportion of an electrode can be formed on a major surface of each z-axisportion 202, 203 of the proof mass at each electrode end. In someexamples, a second portion of each electrode can be formed on the vialayer near each electrode end of each z-axis portion 202, 203. Eachz-axis portion 202, 203 of the proof mass 200 can include a pair ofelectrodes. In certain examples, the pairs of electrodes can becomplementary. Complementary electrodes can assist in eliminatingresidual effects of proof mass stress that can be present duringoperation of the sensor, can be present due to manufacturing variationsof the proof mass, or can be present due to assembly operations of thesensor.

In the presence of an acceleration along the x-axis, the y-axis frame251 and the x-axis frame 252 can move in unison with respect to theanchor region 204. The resulting motion can be detected using the x-axisaccelerometer sense electrodes 211 located on opposite sides of theproof-mass, allowing differential measurement of deflections. In variousexamples, a variety of detection methods, such as capacitive (variablegap or variable area capacitors), piezoelectric, piezoresistive,magnetic or thermal can be used.

In the presence of an acceleration along the y-axis, the y-axis flexurebearings 210 that connect the y-axis frame 251 to the x-axis frame 252can deflect and allow the y-axis frame 251 to move along the y-axis inunison with the proof-mass 200, while the x-axis frame 252 remainsstationary. The resulting motion can be detected using the y-axisaccelerometer sense electrodes 212 located on opposite sides of theproof-mass, allowing differential measurement of deflections. In variousexamples, a variety of detection methods, such as capacitive (variablegap or variable area capacitors), piezoelectric, piezoresistive,magnetic or thermal can be used.

FIG. 2B illustrates generally a perspective view of an example proofmass 200 including split z-axis portions 202, 203. In certain examples,the proof mass 200 can include a central portion 201, a first z-axisportion 202, a first hinge 206, a second hinge 216 (not shown in FIG.2B), a second z-axis portion 203, a third hinge 208, and a fourth hinge218 (not shown in FIG. 2B). In an example, the first and second hinges206, 216 can couple the first z-axis portion 202 to the central portion201. In an example, the third and fourth hinges 208, 218 can couple thesecond z-axis portion 203 to the central portion 201. In certainexamples, the third and fourth hinges 208, 218 can be located oppositethe first and second hinges 206, 216 across the central portion 201 ofthe proof mass 200. In certain examples, the hinges 206, 216, 208, 218can asymmetrically couple to their respective z-axis portion 202, 203 toallow adjacent ends of the z-axis portions 202, 203 to move in opposite,out-of-plane directions for a given acceleration along the z-axis. Incertain examples, each z-axis portion 202, 203 includes a firstelectrode end (Z+) and a second electrode end (Z−). In certain examples,an electrode is formed at each electrode end. In some examples, aportion of an electrode can be formed on a major surface of each z-axisportion 202, 203 of the proof mass 200 at each electrode end. In someexamples, a second portion of each electrode can be formed on the vialayer near each electrode end of each z-axis portion. Each z-axisportion 202, 203 can be associated with a pair of electrodes. In certainexamples, the pairs of electrodes can be complementary. Complementaryelectrodes can assist in eliminating residual effects of proof massstress that can be present during operation of the sensor, can bepresent due to manufacturing variations of the proof mass 200, or can bepresent due to assembly operations of a sensor including the proof mass200. In certain examples, the first and second z-axis portions 202, 203can be of substantially the same shape and size. In an example, thefirst and second z-axis portions 202, 203 of the proof mass 200 canenvelop the perimeter of the central portion 201 of the proof mass 200.

In certain examples, the proof mass 200 can include x-axis flexurebearings 209 responsive to acceleration of the proof mass 200 along thex-axis. In such examples, the proof mass 200 can include first portions211 of x-axis electrodes configured to move in relation to second,stationary portions 213 of the x-axis electrodes. In an example, thesecond, stationary portions 213 (not shown in FIG. 2B) of the x-axiselectrodes can be formed of the same device layer material as the proofmass 200. In certain examples, the second, stationary portions 213 ofthe x-axis electrodes can be anchored to an adjacent sensor layer, suchas a via layer, and can include fin type structures configured tointerleave with the fin type structures of the first portions 211 of thex-axis electrodes.

In certain examples, the proof mass can include y-axis flexure bearings210 responsive to acceleration of the proof mass 200 along the y-axis.In such examples, the proof mass 200 can include first portions ofy-axis electrodes 212 configured to move in relation to second,stationary portions 214 of the y-axis electrodes. In an example, thesecond, stationary portions 214 (not shown in FIG. 2B) of the y-axiselectrodes can be formed of the same device layer material as the proofmass 200. In certain examples, the second, stationary portions 214 ofthe y-axis electrodes can be anchored to an adjacent sensor layer, suchas a via layer, and can include fin type structures configured tointerleave with the fin type structures of the first portions 212 of they-axis electrodes.

FIG. 3A illustrates generally an example proof mass 300 including asplit z-axis portions 302, 303, a central portion 301 and hinges 306,316, 308, 318 for coupling the split z-axis portions 302, 303 to thecentral portion 301. In certain examples, the proof mass 300 can beanchored to an adjacent sensor layer via an anchor region 304 of thecentral portion 301 of the proof mass 300. In certain examples, theproof mass 300 can be used to measure acceleration along a z-axis usingout-of-plane movement of the split z-axis portions 302, 303 of the proofmass 300. In some examples, the proof mass 300 can be used to detectacceleration along multiple axes. In some examples, the proof mass 300can includes portions 311, 312 of electrodes to detect accelerationalong the x and y axes. In certain examples, the proof mass 300 caninclude x-axis flexure bearings 309 that can respond to accelerationalong an x direction, and y-axis flexure bearings 310 that can respondto acceleration along a y direction. Electrodes to detect thedeformation of the x and y flexure bearings 309, 310 can be formed, inpart, using the proof mass 300, and stator structures (not shown)anchored to an adjacent layer of an acceleration sensor. In certainexamples, the split z-axis portions 302, 303 of the proof mass 300 caninclude a first z-axis portion 302 and a second z-axis portion 303. Thefirst z-axis portion 302 can be coupled to the central portion 301 usinga first hinge 306 and a second hinge 316. The second z-axis portion 303can be coupled to the central portion 301 of the proof mass 300 using athird hinge 308 and a fourth hinge 318. In certain examples, the use oftwo hinges to couple one of the z-axis portions to the central portioncan make the z-axis portion more resistant to movement in the x and ydirections. Movement in the x and y directions of the z-axis proof massportions 302, 303 can cause misalignment of the z-axis electrodes and,in turn, can lead to less accurate z-axis acceleration measurement.

In certain examples, each pair of hinges 306 and 316, 308 and 318 canasymmetrically couple their respective z-axis portion 302, 303 to thecentral portion 301 to allow adjacent ends of the z-axis portions 302,303 to move in opposite, out-of-plane directions for a givenacceleration along the z-axis. In certain examples, each z-axis portion302, 303 can include a first electrode end (Z+) and a second electrodeend (Z−). In certain examples, an electrode can be formed at eachelectrode end. In some examples, a portion of an electrode can be formedon a major surface of each z-axis portion 302, 303 of the proof mass 300at each electrode end. In some examples, a second portion of eachelectrode can be formed on the via layer near each electrode end of eachz-axis portion. Each z-axis portion 302, 303 of the proof mass 300 caninclude a pair of electrodes. In certain examples, the two pairs ofz-axis electrodes can be complementary. Complementary z-axis electrodescan assist in eliminating residual effects of proof mass stress that canbe present during operation of the sensor, can be present due tomanufacturing variations of the proof mass 300, or can be present due toassembly operations of a sensor including the proof mass 300.

FIG. 3B illustrates generally a perspective view of an example proofmass 300 including split z-axis portions 302, 303. In certain examples,the proof mass 300 can include a central portion 301, a first z-axisportion 302, a first hinge 306, a second hinge 316, a second z-axisportion 303, a third hinge 308, and a fourth hinge 318. In an example,the first and second hinges 306, 316 can couple the first z-axis portion302 to the central portion 301. In an example, the third and fourthhinges 308, 318 can couple the second z-axis portion 303 to the centralportion 301. In certain examples, the third and fourth hinges 308, 318can be located opposite the first and second hinges 306, 316 across thecentral portion 301 of the proof mass 300. In certain examples, thehinges 306, 316, 308, 318 can asymmetrically couple their respectivez-axis portion 302, 303 to allow adjacent ends of the z-axis portions tomove in opposite, out-of-plane directions for a given acceleration alongthe z-axis. In certain examples, each z-axis portion 302, 303 caninclude a first electrode end (Z+) and a second electrode end (Z−). Incertain examples, an electrode is formed at each electrode end. In someexamples, a portion of an electrode can be formed on a major surface ofeach z-axis portion 302, 303 of the proof mass 300 at each electrodeend. In some examples, a second portion of each electrode can be formedon the via layer near each electrode end of each z-axis portion 302,303. Each z-axis portion 302, 303 can include a pair of electrodes. Incertain examples, the pairs of electrodes can be complementary.Complementary electrodes can assist in eliminating residual effects ofproof mass stress that can be present during operation of the sensor,can be present due to manufacturing variations of the proof mass 300, orcan be present due to assembly operations of a sensor including theproof mass 300. In an example, the first and second z-axis portions 302,303 of the proof mass can envelop the perimeter of the central portion301 of the proof mass 300. In an example, the first z-axis portion 302of the proof mass 300 can envelop at least a portion of the electrodeends of the second z-axis portion 303 of the proof mass 300.

In certain examples, the proof mass 300 can include x-axis flexurebearings 309 responsive to acceleration of the proof mass 300 along thex-axis. In such examples, the proof mass 300 can include first portions311 of x-axis electrodes configured to move in relation to second,stationary portions of the x-axis electrodes. In an example, the second,stationary portions (not shown in FIG. 3B) of the x-axis electrodes canbe formed of the same device layer material as the proof mass. Incertain examples, the second, stationary portions of the x-axiselectrodes can be anchored to an adjacent sensor layer, such as a vialayer, and can include fin type structures configured to interleave withthe fin type structures of the first portions 311 of the x-axiselectrodes.

In certain examples, the proof mass can include y-axis flexure bearings310 responsive to acceleration of the proof mass 300 along the y-axis.In such examples, the proof mass 300 can include first portions 312 ofy-axis electrodes configured to move in relation to second, stationaryportions of the y-axis electrodes. In an example, the second, stationaryportions (not shown in FIG. 3B) of the y-axis electrodes can be formedof the same device layer material as the proof mass 300. In certainexamples, the second, stationary portions of the y-axis electrodes canbe anchored to an adjacent sensor layer, such as a via layer, and caninclude fin type structures configured to interleave with the fin typestructures of the first portions 312 of the y-axis electrodes.

FIG. 4 illustrates generally an example of a 3+3-degrees-of-freedom(3+3DOF) inertial measurement unit (IMU) 450 (e.g., a 3-axis gyroscopeand a 3-axis accelerometer), such as formed in a single plane of adevice layer of an IMU. In an example, the 3+3 DOF can include a 3-axisgyroscope 420 and a 3-axis accelerometer 400 on the same wafer.

In this example, each of the 3-axis gyroscope 420 and the 3-axisaccelerometer 400 have separate proof-masses, though when packaged, theresulting device (e.g., chip-scale package) can share a cap, and thus,the 3-axis gyroscope 420 and the 3-axis accelerometer 400 can reside inthe same cavity. Moreover, because the devices can be formed at similartimes and on similar materials, the invention can significantly lowerthe risk of process variations, can reduce the need to separatelycalibrate the sensors, can reduce alignment issues, and can allow closerplacement of the two devices than separately bonding the devices nearone another.

In addition, there can be a space savings associated with sealing theresulting device. For example, if a given seal width is used to sealeach of the device individually, sharing the cap wafer and reducing thedistance between devices allows the overall size of the resulting deviceto shrink. Packaged separately, the amount of space required for theseal width could double.

In an example, the 3-axis gyroscope 420 can include a single proof-massproviding 3-axis gyroscope operational modes patterned into a devicelayer of the 3-DOF IMU 440.

In an example, the single proof-mass can be suspended at its centerusing a single central anchor (e.g., anchor 434) and a centralsuspension 435 including symmetrical central flexure bearings(“flexures”), such as disclosed in the copending Acar et al., PCT PatentApplication Serial No. US2011052006, entitled “FLEXURE BEARING TO REDUCEQUADRATURE FOR RESONATING MICROMACHINED DEVICES,” filed on Sep. 16,2011, which is hereby incorporated by reference in its entirety. Thecentral suspension 435 can allow the single proof-mass to oscillatetorsionally about the x, y, and z axes, providing three gyroscopeoperational modes, including:

(1) Torsional in-plane drive motion about the z-axis;

(2) Torsional out-of-plane y-axis gyroscope sense motion about thex-axis; and

(3) Torsional out-of-plane x-axis gyroscope sense motion about they-axis. Further, the single proof-mass design can be composed ofmultiple sections, including, for example, a main proof-mass section 436and x-axis proof-mass sections 437 symmetrical about the y-axis. In anexample, drive electrodes 438 can be placed along the y-axis of the mainproof-mass section 436. In combination with the central suspension 435,the drive electrodes 438 can be configured to provide a torsionalin-plane drive motion about the z-axis, allowing detection of angularmotion about the x and y axes.

In an example, the x-axis proof-mass sections 437 can be coupled to themain proof-mass section 436 using z-axis gyroscope flexure bearings 440.In an example, the z-axis gyroscope flexure bearings 440 can allow thex-axis proof-mass sections 437 to oscillate linear anti-phase in thex-direction for the z-axis gyroscope sense motion.

Further, the 3-axis inertial sensor 450 can include z-axis gyroscopesense electrodes 441 configured to detect anti-phase, in-plane motion ofthe x-axis proof-mass sections 437 along the x-axis.

In an example, each of the drive electrodes 438 and z-axis gyroscopesense electrodes 441 can include moving fingers coupled to one or moreproof-mass sections interdigitated with a set of stationary fingersfixed in position (e.g., to the via wafer) using a respective anchor,such as anchors 439, 442. In an example, the drive electrodes 438 of thegyroscope can include a set of moving fingers coupled to the mainproof-mass section 436 interdigitated with a set of stationary fingersfixed in position using a first drive anchor 439 (e.g., a raised andelectrically isolated portion of the via wafer). In an example, thestationary fingers can be configured to receive energy through the firstdrive anchor 439, and the interaction between the interdigitated movingand stationary fingers of the drive electrodes 438 can be configured toprovide an angular force to the single proof-mass about the z-axis.

In an example, the drive electrodes 438 are driven to rotate the singleproof-mass about the z-axis while the central suspension 435 providesrestoring torque with respect to the fixed anchor 434, causing thesingle proof-mass to oscillate torsionally, in-plane about the z-axis ata drive frequency dependent on the energy applied to the driveelectrodes 438. In certain examples, the drive motion of the singleproof-mass can be detected using the drive electrodes 438.

In the presence of an angular rate about the x-axis, and in conjunctionwith the drive motion of the 3-axis gyroscope 420, Coriolis forces inopposite directions along the z-axis can be induced on the x-axisproof-mass sections 437 because the velocity vectors are in oppositedirections along the y-axis. Thus, the single proof-mass can be excitedtorsionally about the y-axis by flexing the central suspension 435. Thesense response can be detected using out-of-plane x-axis gyroscope senseelectrodes, e.g., formed in the via wafer and using capacitive couplingof the x-axis proof-mass sections 437 and the via wafer.

In the presence of an angular rate about the y-axis, and in conjunctionwith the drive motion of the 3-axis gyroscope 420, Coriolis forces inopposite directions along the z-axis can be induced on the mainproof-mass section 436 because the velocity vectors are in oppositedirections along the x-axis. Thus, the single proof-mass can be excitedtorsionally about the x-axis by flexing the central suspension 435. Thesense response can be detected using out-of-plane y-axis gyroscope senseelectrodes, e.g., formed in the via wafer and using capacitive couplingof the main proof-mass section 436 and the via wafer.

In the presence of an angular rate about the z-axis, and in conjunctionwith the drive motion of the 6-axis inertial sensor 450, Coriolis forcesin opposite directions along the x-axis can be induced on the x-axisproof-mass sections 437 because the velocity vectors are in oppositedirections along the y-axis. Thus, the x-axis proof-mass sections 437can be excited linearly in opposite directions along the x-axis byflexing the z-axis flexure bearings 440 in the x-direction. Further, thez-axis gyroscope coupling flexure bearings 443 can be used to provide alinear anti-phase resonant mode of the x-axis proof-mass sections 437,which are directly driven by the anti-phase Coriolis forces.

The sense response can be detected using in-plane parallel-plate senseelectrodes, such as the z-axis gyroscope sense electrodes 441 formed inthe device layer 105.

During the anti-phase motion, the connection beams that connect the twox-axis proof-mass sections 437 to the z-axis gyroscope coupling flexurebearing 443 apply forces in the same direction and the coupling beamsundergo a natural bending with low stiffness.

In contrast, during the in-phase motion, the coupling beams of thez-axis gyroscope coupling flexure bearing 443 apply forces in oppositedirections on the coupling beams, forcing the coupling beams into atwisting motion with a higher stiffness. Thus, the in-phase motionstiffness and the resonant frequencies are increased, providing improvedvibration rejection.

FIG. 5 illustrates generally a schematic cross sectional view of a3-degrees-of-freedom (3-DOF) inertial measurement unit (IMU) 500, suchas a 3-DOF gyroscope or a 3-DOF micromachined accelerometer, formed in achip-scale package including a cap wafer 501, a device layer 505including micromachined structures (e.g., a micromachined 3-DOF IMU),and a via wafer 503. In an example, the device layer 505 can besandwiched between the cap wafer 501 and the via wafer 503, and thecavity between the device layer 505 and the cap wafer 501 can be sealedunder vacuum at the wafer level.

In an example, the cap wafer 501 can be bonded to the device layer 505,such as using a metal bond 502. The metal bond 502 can include a fusionbond, such as a non-high temperature fusion bond, to allow getter tomaintain long term vacuum and application of anti-stiction coating toprevent stiction that can occur to low-g acceleration sensors. In anexample, during operation of the device layer 505, the metal bond 502can generate thermal stress between the cap wafer 501 and the devicelayer 505. In certain examples, one or more features can be added to thedevice layer 505 to isolate the micromachined structures in the devicelayer 505 from thermal stress, such as one or more stress reducinggrooves formed around the perimeter of the micromachined structures. Inan example, the via wafer 503 can be bonded to the device layer 505,such as fusion bonded (e.g., silicon-silicon fusion bonded, etc.), toobviate thermal stress between the via wafer 503 and the device layer505.

In an example, the via wafer 503 can include one or more isolatedregions, such as a first isolated region 507, isolated from one or moreother regions of the via wafer 503, for example, using one or morethrough-silicon-vias (TSVs), such as a first TSV 508 insulated from thevia wafer 503 using a dielectric material 509. In certain examples, theone or more isolated regions can be utilized as electrodes to sense oractuate out-of-plane operation modes of the 6-axis inertial sensor, andthe one or more TSVs can be configured to provide electrical connectionsfrom the device layer 505 outside of the system 500. Further, the viawafer 503 can include one or more contacts, such as a first contact 550,selectively isolated from one or more portions of the via wafer 503using a dielectric layer 504 and configured to provide an electricalconnection between one or more of the isolated regions or TSVs of thevia wafer 503 to one or more external components, such as an ASIC wafer,using bumps, wire bonds, or one or more other electrical connection.

In certain examples, the 3-degrees-of-freedom (3-DOF) gyroscope or themicromachined accelerometer in the device layer 505 can be supported oranchored to the via wafer 503 by bonding the device layer 505 to aprotruding portion of the via wafer 503, such as an anchor 506. In anexample, the anchor 506 can be located substantially at the center ofthe via wafer 503, and the device layer 505 can be fusion bonded to theanchor 506, such as to eliminate problems associated with metal fatigue.

Additional Notes

In Example 1, a proof mass, for an accelerometer for example, caninclude a center portion configured to anchor the proof-mass to anadjacent layer, a first z-axis portion configure to rotate about a firstaxis using a first hinge, the first axis parallel to an x-y planeorthogonal to a z-axis, a second z-axis portion configure to rotateabout a second axis using a second hinge, the second axis parallel tothe x-y plane; wherein the first z-axis portion is configured to rotateindependent of the second z-axis portion.

In Example 2, the first z-axis portion of Example 1 optionally isconfigured to rotate in an opposite direction than that of the secondz-axis portion in response to an acceleration of the proof mass alongthe z-axis. In Example 3, the first hinge of any one or more of Examples1-2 optionally is located opposite the second hinge with respect to thecentral portion.

In Example 4, the first hinge of any one or more of Examples 1-3optionally is coupled to the first z-axis portion closer to a first endof the first z-axis portion than a second end of the first z-axisportion.

In Example 5, the second hinge of any one or more of Examples 1-4optionally is coupled to the second z-axis portion closer to a first endof the second z-axis portion than a second end of the axis z-axisportion.

In Example 6, the proof mass of any one or more of Examples 1-5optionally includes a third hinge, wherein the first z-axis portion isconfigured to rotate about the first axis in the x-y plane using thefirst hinge and the third hinge.

In Example 7, the proof mass of any one or more of Examples 1-6optionally includes a fourth hinge, wherein the second z-axis portion isconfigured to rotate about the second axis in the x-y plane using thesecond hinge and the fourth hinge.

In Example 8, the central portion of any one or more of Examples 1-7optionally includes an anchor portion and an x-axis proof mass portion,the x-axis proof mass portion configured to deflect, with respect to theanchor portion, in response to an acceleration of the proof mass alongthe x-axis.

In Example 9, the central portion of any one or more of Examples 1-8optionally includes a y-axis proof mass portion, the y-axis proof massportion configured to deflect, with respect to the anchor portion, inresponse to an acceleration of the proof mass along the y-axis.

In Example 10, the first z-axis portion and the second z-axis portion ofany one or more of Examples 1-9 optionally substantially envelop thecentral portion in the x-y-plane.

In Example 11, a method can include accelerating a proof mass along az-axis direction, rotating a first z-axis portion of the proof mass in afirst rotational direct about a first axis lying in an x-y-plane using afirst hinge, the rotation of the first z-axis portion of the proof massresponsive to the acceleration of the proof mass in the z-axisdirection, and rotating a second z-axis portion of the proof mass in asecond rotational direct about a second axis lying in an x-y-plane usinga second hinge, the rotation of the second z-axis portion of the proofmass responsive to the acceleration of the proof mass in the z-axisdirection. The first rotational direction can be opposite the secondrotational direction using a point of reference outside a perimeter ofthe proof mass.

In Example 12, an apparatus can include a single proof massaccelerometer, the single proof mass accelerometer including a singleproof mass formed in the x-y plane of a device layer, the single proofmass including, a central portion including a single, central anchor, afirst z-axis portion configure to rotate about a first axis in the x-yplane using a first hinge, the first hinge coupled to the centralportion, and a second z-axis portion configure to rotate about a secondaxis in the x-y plane using a second hinge, the second hinge coupled tothe central portion. The first z-axis portion can be configured torotate independent of the second z-axis portion. The single centralanchor can be configured to suspend the single proof-mass. The centralportion can include separate x, y, axis flexure bearings, wherein the xand y-axis flexure bearings are symmetrical about the single, centralanchor.

In Example 13, the central portion of any one or more of Examples 1-12optionally includes in-plane x and y-axis accelerometer sense electrodessymmetrical about the single, central anchor.

In Example 14, the single proof mass of any one or more of Examples 1-13optionally includes a first portion of first and second out-of-planez-axis accelerometer sense electrodes coupled to the first z-axisportion, and a first portion of third and fourth out-of-plane z-axissense electrodes coupled to the second z-axis portion.

In Example 15, the apparatus of any one or more of Examples 1-14optionally includes a cap wafer bonded to a first surface of the devicelayer, and a via wafer bonded to a second surface of the device layer,wherein the cap wafer and the via wafer are configured to encapsulatethe single proof mass accelerometer in a cavity.

In Example 16, the via wafer of any on or more of Examples 1-15optionally includes a second portion of the first and secondout-of-plane z-axis accelerometer sense electrodes, and a second portionof the third and fourth out-of-plane z-axis sense electrodes.

In Example 17, the apparatus of any one or more of Examples 1-16optionally includes a first portion of x-axis accelerometer electrodescoupled to the device layer, wherein the central portion of the singleproof mass includes a second portion of the x-axis accelerometerelectrodes, the second portion of the x-axis electrodes coupled to thesingle central anchor using the x flexure bearings.

In Example 18, the apparatus of any one or more of Examples 1-17optionally includes a first portion of y-axis accelerometer electrodescoupled to the device layer, and the central portion of the single proofmass includes a second portion of the y-axis accelerometer electrodes,the second portion of the y-axis electrodes coupled to the singlecentral anchor using the y flexure bearings.

In Example 19, The apparatus of any one or more of Examples 1-18optionally includes a multiple-axis gyroscope within the cavity andadjacent the single proof mass accelerometer. The multiple-axisgyroscope optionally includes a second single proof-mass formed in thex-y plane of the device layer. The second single proof-mass can includea main proof-mass section suspended about a second single, centralanchor, the main proof-mass section including a radial portion extendingoutward towards an edge of the multiple-axis gyroscope, a centralsuspension system configured to suspend the second single proof massfrom the single, central anchor, and a drive electrode including amoving portion and a stationary portion, the moving portion coupled tothe radial portion, wherein the drive electrode and the centralsuspension system are configured to oscillate the single proof massabout the z-axis normal to the x-y plane at a drive frequency.

In Example 20, wherein the second, single proof mass of any one or moreof Examples 1-19 optionally includes symmetrical x-axis proof-masssections configured to move anti-phase along the x-axis in response toz-axis angular motion.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. In some examples, the above-described examples (or one ormore aspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A proof-mass structure for an accelerometer, the proof mass structureconfigured to couple to an adjacent layer using a single anchor, theproof mass structure comprising: a first z-axis portion configured torotate about a first axis using a first hinge, the first axis parallelto an x-y plane orthogonal to a z-axis; a second z-axis portionconfigured to rotate about a second axis using a second hinge, thesecond axis parallel to the x-y plane; wherein the first z-axis portionis configured to rotate independent of the second z-axis portion; and acentral portion coupled to the first z-axis portion and the secondz-axis portion via the first hinge and the second hinge, respectively,the central portion configured to couple with the single anchor and tosuspend the first z-axis portion and the second z-axis portion fromadjacent layers of the accelerometer.
 2. The proof mass of claim 1,wherein the first z-axis portion is configured to rotate in an oppositedirection than that of the second z-axis portion in response to anacceleration of the proof mass along the z-axis.
 3. The proof mass ofclaim 1, wherein the first hinge is located opposite the second hingewith respect to the central portion.
 4. The proof mass of claim 1,wherein the first hinge is coupled to the first z-axis portion closer toa first end of the first z-axis portion than a second end of the firstz-axis portion.
 5. The proof mass of claim 1, wherein the second hingeis coupled to the second z-axis portion closer to a first end of thesecond z-axis portion than a second end of the axis z-axis portion. 6.The proof mass of claim 1, including a third hinge, wherein the firstz-axis portion is configured to rotate about the first axis in the x-yplane using the first hinge and the third hinge.
 7. The proof mass ofclaim 1, including a fourth hinge, wherein the second z-axis portion isconfigured to rotate about the second axis in the x-y plane using thesecond hinge and the fourth hinge.
 8. The proof mass of claim 1, whereinthe central portion includes an anchor portion and an x-axis proof massportion, the x-axis proof mass portion configured to deflect, withrespect to the anchor portion, in response to an acceleration of theproof mass along the x-axis.
 9. The proof mass of claim 8, wherein thecentral portion includes a y-axis proof mass portion, the y-axis proofmass portion configured to deflect, with respect to the anchor portion,in response to an acceleration of the proof mass along the y-axis. 10.The proof mass of claim 1 wherein the first z-axis portion and thesecond z-axis portion substantially envelop the central portion in thex-y-plane.
 11. A method comprising: suspending a proof mass structure ofan accelerometer from adjacent layers of an accelerometer using a singleanchor and a central portion of the proof mass structure, the proof massstructure including a first z-axis portion and a second z-axis portion,wherein the first z-axis portion of the proof mass structure and thesecond z-axis portion of the proof mass structure are coupled to thecentral portion; accelerating the proof mass structure along a z-axisdirection; rotating the first z-axis portion of the proof mass in afirst rotational direction about a first axis lying in an x-y-planeusing a first hinge, the rotation of the first z-axis portion of theproof mass responsive to the acceleration of the proof mass in thez-axis direction; and rotating the second z-axis portion of the proofmass in a second rotational direct about a second axis lying in anx-y-plane using a second hinge, the rotation of the second z-axisportion of the proof mass responsive to the acceleration of the proofmass in the z-axis direction; and wherein the first rotational directionis opposite the second rotational direction using a point of referenceoutside a perimeter of the proof mass.
 12. An apparatus comprising: asingle proof mass accelerometer, the single proof mass accelerometerincluding: a single accelerometer proof mass formed in the x-y plane ofa device layer, the single proof mass including: a central portionincluding: a single, central anchor, configured to suspend the singleproof-mass from adjacent layers of the apparatus a first z-axis portionconfigured to rotate about a first axis in the x-y plane using a firsthinge, the first hinge coupled to the central portion; a second z-axisportion configure to rotate about a second axis in the x-y plane using asecond hinge, the second hinge coupled to the central portion; whereinthe first z-axis portion is configured to rotate independent of thesecond z-axis portion.
 13. The apparatus of claim 12, wherein thecentral portion includes in-plane x and y-axis accelerometer senseelectrodes symmetrical about the single, central anchor.
 14. Theapparatus of claim 12, wherein the single proof mass includes: a firstportion of first and second out-of-plane z-axis accelerometer senseelectrodes coupled to the first z-axis portion, and a first portion ofthird and fourth out-of-plane z-axis sense electrodes coupled to thesecond z-axis portion.
 15. The apparatus of claim 14, including: a capwafer bonded to a first surface of the device layer; and a via waferbonded to a second surface of the device layer, wherein the cap waferand the via wafer are configured to encapsulate the single proof massaccelerometer in a cavity.
 16. The apparatus of claim 15, wherein thevia wafer includes: a second portion of the first and secondout-of-plane z-axis accelerometer sense electrodes, and a second portionof the third and fourth out-of-plane z-axis sense electrodes.
 17. Theapparatus of claim 16, including a first portion of x-axis accelerometerelectrodes coupled to the device layer, and wherein the central portionof the single proof mass includes a second portion of the x-axisaccelerometer electrodes, the second portion of the x-axis accelerometerelectrodes coupled to the single central anchor using the x flexurebearings.
 18. The apparatus of claim 16, including a first portion ofy-axis accelerometer electrodes coupled to the device layer, and whereinthe central portion of the single proof mass includes a second portionof the y-axis accelerometer electrodes, the second portion of the y-axisaccelerometer electrodes coupled to the single central anchor using they flexure bearings.
 19. The apparatus of claim 15, including amultiple-axis gyroscope within the cavity and adjacent the single proofmass accelerometer, the multiple-axis gyroscope including: a singlegyroscope proof-mass formed in the x-y plane of the device layer, thesecond single proof-mass including: a main proof-mass section suspendedabout a second single, central anchor, the main proof-mass sectionextending outward towards an edge of the multiple-axis gyroscope; acentral suspension system configured to suspend the single gyroscopeproof mass from the single, central anchor; and a drive electrodeincluding a moving portion and a stationary portion, the moving portionincluding a first set of fingers interdigitated with a second set offingers of the stationary portion, wherein the drive electrode and thecentral suspension system are configured to oscillate the single proofmass about the z-axis normal to the x-y plane at a drive frequency. 20.The apparatus of claim 19, wherein the single gyroscope proof massincludes symmetrical x-axis proof-mass sections configured to moveanti-phase along the x-axis in response to z-axis angular motion.